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Novel streptococcus thermophilus strains producing stable high-molecular-mass exopolysaccharides

a high-molecular mass, heteropolysaccharide technology, applied in the field of streptococcus thermophilus strains producing stable high-molecular mass heteropolysaccharides, can solve the problems of unstable production, low amount of eps produced by labs, and not all food additives are allowed in all countries, so as to achieve enhanced growth and eps production, and improve solubility. , the effect of good growth

Inactive Publication Date: 2005-09-22
VRIJE UNIV BRUSSEL
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Benefits of technology

The present invention relates to a new strain of Streptococcus thermophilus, designated ST 111, which produces a high-molecular-mass exopolysaccharide during fermentation. This exopolysaccharide has been deposited at the BCCM in Belgium and is currently available for use in fermented food products. The invention also includes a functional starter culture or co-culture containing this strain, which can be used to improve the texture, water retention, and decrease syneresis of fermented products. The high-molecular-mass exopolysaccharide can also be used as an additive to food products to improve their water retention and texture.

Problems solved by technology

However, not all these food additives are allowed in all countries.
Furthermore, the amounts of EPS produced by LAB are low and their production is unstable, particularly in milk (Degeest et al., 2001b).
Due to the low amount of EPS produced by LAB strains and the transitory nature of the exopolysaccharide trait (Cerning, 1990), the use of these compounds as food-grade additives is still limited.
However, the use of genetically modified microorganisms in the food industry is hindered by the hostility of the consumer.

Method used

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  • Novel streptococcus thermophilus strains producing stable high-molecular-mass exopolysaccharides
  • Novel streptococcus thermophilus strains producing stable high-molecular-mass exopolysaccharides
  • Novel streptococcus thermophilus strains producing stable high-molecular-mass exopolysaccharides

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Experimental program
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example 1

Materials and Methods

Strain and Strain Propagation.

[0114]Streptococcus thermophilus ST 111 was used as the EPS-producing strain. The strain was disposed on May 29, 2002 under the accession number LMG P-21524 at the Belgian Coordinated Collections of Microorganisms (BCCM / LMG culture collection).

[0115] The strain was stored at −80° C. in de Man-Rogosa-Sharpe (MRS) medium (Oxoid, Basingstoke, United Kingdom). To obtain exponentially growing cultures, S. thermophilus ST 111 was propagated twice at 42° C. for 12 h in the medium identical to the one used for the fermentations later on.

Media

[0116] In MRS medium (de Man et al., 1960), M17 medium (Terzaghi & Sandine, 1975), and HJL medium (Stingele et al., 1996), lactose, sucrose, glucose, galactose, fructose, and rhamnose were first tested as the sole energy source (2.0%, m / v) for growth of S. thermophilus ST 111 on 10-ml scale. Then, different media were tested in Erlenmeyer flasks on 50-ml scale as to their capacity to support grow...

example 2

Characterisation of EPS

Molecular Mass Determination of EPS

[0121] The EPS material isolated as described above was dissolved in MilliQ water (Millipore Corp., Bedford, Mass., USA), dialysed against distilled water at 4° C. for four days with water replacement twice a day, using Spectra / Por membranes (VWR International) with a MMCO of 3500 Da, and subsequently freeze-dried.

[0122] The molecular mass of the isolated EPS of all fermentations was determined by gel permeation chromatography. A Sephacryl S-400 gel (Amersham BioSciences AB, Uppsala, Sweden) was used. Samples containing about 50 mg.ml−1 of lyophilised EPS were applied. The EPS were eluted with 50 mM potassium phosphate / NaOH buffer (pH 6.8) containing 0.15 M NaCl. A dextran standard series (molecular masses between 8.0×104 and 1.8×106 Da) was used to estimate the EPS molecular mass. The polysaccharide content was determined by on line refractive index detection (Waters refractive index detector, Waters Corp., Milford, Mass...

example 3

Growth and Exopolysaccharide Production Kinetics of S. thermophilus ST 111

[0126]S. thermophilus ST 111 only grew in MRS, M17, and HJL media supplemented with glucose, lactose, and sucrose as the sole energy source. On 50-ml scale it was observed that EPS production was comparable in all three media when 2.0% of lactose was used, with an increase in EPS yield for higher lactose concentrations. In milk medium, both growth and EPS production were enhanced when an additional energy or nitrogen source were applied. Contaminating polysaccharide material from medium constituents was present in all complex media, except in milk (Table 1).

[0127]S. thermophilus ST 111 displayed a very low proteolytic activity, as indicated by its slow coagulation of milk at a suboptimal growth temperature of 30° C. Further, fermentation in milk alone with S. thermophilus ST 111 only slightly improved the viscosity of the medium. During fermentations performed in milk medium at 37° C. with pH control, S. the...

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Abstract

The invention relates to the field of exopolysaccharide producing lactic acid bacteria. The invention relates to methods and culture media for producing large amounts of exopolysaccharides in safe and simple fermentation conditions. The invention more specifically relates to the characterization of a Streptococcus thermophilus ST 111 strain producing a stable high-molecular-mass heteropolysaccharide, its use in functional starter cultures and its use in food fermentation processes such as processes producing milk products, yoghurt and cheese for texture improvement and decreasing syneresis during fermentation and in the fermented product.

Description

FIELD OF THE INVENTION [0001] The invention relates to the field of methods for producing large amounts of exopolysaccharides. The invention more specific relates to the characterization of a Streptococcus thermophilus strain producing a stable high-molecular-mass heteropolysaccharide, and to the use of said Streptococcus thermophilus strain in and as functional starter culture and in the production of dairy products. BACKGROUND OF THE INVENTION [0002] Sugar polymers or exopolysaccharides (EPS) produced by lactic acid bacteria (LAB) can be subdivided into two groups: homopolysaccharides and heteropolysaccharides (Cerning, 1990, 1995; De Vuyst & Degeest, 1999). Four groups of homopolysaccharides can be distinguished: α-D-glucans, β-D-glucans, β-D-fructans, and others like polygalactan (Monsan et al., 2001). Strain-specific differences occur that depend on the degree of branching and the different linking sides. Heteropolysaccharides are produced by LAB in a greater variety concerning...

Claims

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Application Information

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Patent Type & Authority Applications(United States)
IPC IPC(8): A23C9/12A23C9/123C08B37/00C12N1/20C12P19/04
CPCA23C9/1238A23C2220/206C12R1/46C12P19/04A23Y2240/75C12R2001/46C12N1/205A23V2400/249
Inventor DE VUYST, LUCVANINGELGEM, FREDERIK
Owner VRIJE UNIV BRUSSEL
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